A bit out of the asked age range (I'm 20) but I would like to share my thoughts on this topic as someone who wasn't on MySpace or similar websites.
First of all: I've had enough of the direction that mainstream social media is heading. I don't want to scroll trough AI generated trash pushed to me by some algorithm. There is little to no human creativity on sites like TikTok, everything is a copy of something. And whenever someone posts something unique, I don't see it because whatever I see is chosen by a computer. I can't search something on YouTube because it shows me content that I've already seen, unrelated videos and only one or two actual videos that fit my search. Pinterest is filled with AI generated images and ads, I can't go two seconds without encountering one or the other.
Don't get me started on the ads! I constantly feel like I'm being advertised to. I had to install adblock on my laptop, and half the pages are blank. But I can't install adblock on my phone, so I'm stuck watching and hearing hundreds of ads everyday while I'm doing anything on my phone.
Secondly: the TikTokification of everything. I leave the app because I can't stand the short-form content. So I go on YouTube for long-form content, but YouTube keeps pushing me to watch Shorts. And I heard that Instagram has Reals (I don't have Instagram so I haven't seen this myself). Why does every social media website have its own form of short-form content. They keep copying each other, so why even bother having multiple accounts on multiple apps if they're just going to show me the same type of content.
Also: mainstream social media is also really corporate. You can't personalize you're account any further than your profile picture, banner, username and bio. I miss when you could customize everything on your account. I vaguely remember websites with custom cursors, and how cool they were to me when I was a child. Whenever I used to go online as a child I was amazed by the awesome websites there were. Everyone seemed to have their own website with cool things that interested them and they were passionate about. Now everybody likes the same stuff and talks about the same 3 things.
Everything is boring and overstimulating, with so much ads fighting for your attention. Problems that the old internet didn't have. And I'm having so much fun! I haven't had this much fun online in a long time. And connecting with people that have similar feeling is amazing!
English isn't my first language so please don't mind any spelling mistakes! Thanks for reading. Sorry it's a long comment, I'm quite passionate about this subject to say the least haha.
TLDR: I'm fed up with social media, so I started searching for other options. And the old internet didn't have these problems. Meaning that I had to return to the old internet (and websites inspired by the old web) if I wanted to connect with people but avoid the problems of the modern web.